A classic Chicago candy company will be moving into the city's Old Post Office downtown.

Thursday, city officials will announce the Ferrara Candy Company is moving its headquarters and 400 jobs from Oakbrook Terrace to Chicago.

Ferrara is one of the fastest growing confections companies in the country. The candy giant owns 35 brands including Sweet Tarts, Crunch, Butterfinger, Lemonheads, Red Hots and more. The company will join Walgreens as the second tenant at the re-developed Post Office on Congress Parkway.

"As we planned our move downtown, we sought a workspace that could accommodate our continued growth and help us build a highly differentiated and meaningful employee experience that allows us to continue to attract, retain and inspire best-in-class talent," said Todd Siwak, CEO of Ferrara Candy Company.

Ferrara was founded in 1908 in the city's Little Village neighborhood. It is currently headquartered in Oakbrook Terrace, where they have been since 1960.

A classic Chicago candy company is moving into the city's Old Post Office.

Ferrara decided to move downtown after an employee told Mayor Rahm Emanuel he should talk to the company's CEO. Two days later he called to set up a meeting.

"It's quite literally the gateway to Chicago - close to thoroughfares and transportation hubs. And over time it will house world class amenities that our employees will enjoy using," Siwak said.

The transition should be finished by next summer.

"Today we are not just welcoming 400 new jobs to Chicago, we are welcoming a great company with deep roots in Chicago back home," Emanuel said. "Chicago not only leads the country in corporate relocations every year for the last five years, but we lead the country in the growth of jobs in the food industry. We are glad that a company that had been part of Chicago's past will now be part of our city's future."

The new headquarters will occupy 77,000 square feet inside of the old Chicago main post office at 433 West Van Buren. Both the company and the city say they cannot wait to see life in this unoccupied building.

So far Ferrara and Walgreens have committed to moving into the Old Post Office. The site is more than 12 acres, and the transformation will cost $800 million. Inside, the developers envision open, social spaces, perhaps workout spaces and places to gather.

Mayor Emanuel's office said Ferrara's move is the 63rd food and beverage company to move or expand in Chicago since 2011.